[ovs-dev] [PATCH] ovsdb-idl: Improve comments.
Numan Siddique
nusiddiq at redhat.com
Thu Jun 27 15:41:19 UTC 2019
On Thu, Jun 27, 2019 at 2:32 AM Ben Pfaff <blp at ovn.org> wrote:
> Suggested-by: Numan Siddique <nusiddiq at redhat.com>
> Signed-off-by: Ben Pfaff <blp at ovn.org>
>
Thanks. This is really useful for me.
Acked-by: Numan Siddique <nusiddiq at redhat.com>
> ---
> lib/ovsdb-idl.h | 76 ++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 63 insertions(+), 13 deletions(-)
>
> diff --git a/lib/ovsdb-idl.h b/lib/ovsdb-idl.h
> index 0f5a6d0a27d8..9f12ce3206f3 100644
> --- a/lib/ovsdb-idl.h
> +++ b/lib/ovsdb-idl.h
> @@ -1,4 +1,4 @@
> -/* Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016 Nicira,
> Inc.
> +/* Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2019
> Nicira, Inc.
> * Copyright (C) 2016 Hewlett Packard Enterprise Development LP
> *
> * Licensed under the Apache License, Version 2.0 (the "License");
> @@ -94,29 +94,79 @@ const struct ovsdb_idl_class
> *ovsdb_idl_get_class(const struct ovsdb_idl *);
> const struct ovsdb_idl_table_class *ovsdb_idl_table_class_from_column(
> const struct ovsdb_idl_class *, const struct ovsdb_idl_column *);
>
> -/* Choosing columns and tables to replicate. */
> +/* Choosing columns and tables to replicate.
> + *
> + * The client may choose any subset of the columns and tables to
> replicate,
> + * specifying it one of two ways:
> + *
> + * - As a blacklist (adding the columns or tables to replicate). To do
> so,
> + * the client passes false as 'monitor_everything_by_default' to
> + * ovsdb_idl_create() and then calls ovsdb_idl_add_column() and
> + * ovsdb_idl_add_table() for the desired columns and, if necessary,
> tables.
> + *
> + * - As a whitelist (replicating all columns and tables except those
> + * explicitly removed). To do so, the client passes true as
> + * 'monitor_everything_by_default' to ovsdb_idl_create() and then
> calls
> + * ovsdb_idl_omit() to remove columns.
> + *
> + * There are multiple modes a column may be replicated:
> + *
> + * - Read-only. This is the default. Whenever the column changes in
> any
> + * replicated row, the value returned by ovsdb_idl_get_seqno() will
> change,
> + * letting the client know to look at the replicated data again.
> + *
> + * - Write-only. This is for columns that the client sets and updates
> but
> + * does not want to be alerted about its own updates (which, at the
> OVSDB
> + * level, cannot be distinguished from updates made by any other
> client).
> + * The column will be replicated in the same way as for read-only
> columns,
> + * but the value returned by ovsdb_idl_get_seqno() will not change
> when the
> + * column changes, saving wasted CPU time.
> + *
> + * (A "write-only" client probably does read the column so that it
> can know
> + * whether it needs to update it, but it doesn't expect to react to
> changes
> + * by other clients.)
> + *
> + * To mark a replicated column as write-only, a client calls
> + * ovsdb_idl_omit_alert(). (The column must already be replicated
> one of
> + * the ways described in the previous list.)
> + *
> + * This is an optimization only and does not affect behavioral
> correctness
> + * of an otherwise well-written client.
> + *
> + * - Read/write. In theory, an OVSDB client might both read and write a
> + * column, although OVSDB schemas are usually designed so that any
> given
> + * client only does one or the other. This is actually the same as
> + * read/write columns; that is, the client need take no special
> action.
> + */
>
> -/* Modes with which the IDL can monitor a column.
> +/* Modes with which the IDL can replicate a column. See above comment for
> + * overview.
> *
> - * If no bits are set, the column is not monitored at all. Its value will
> - * always appear to the client to be the default value for its type.
> + * If no bits are set, the IDL does not replicate the column at all. The
> + * client will always see it with the default value for its type.
> *
> - * If OVSDB_IDL_MONITOR is set, then the column is replicated. Its value
> will
> - * reflect the value in the database. If OVSDB_IDL_ALERT is also set,
> then the
> - * value returned by ovsdb_idl_get_seqno() will change when the column's
> value
> - * changes.
> + * If OVSDB_IDL_MONITOR is set, then the IDL replicates the column and
> sets it
> + * to to the value in the database. If OVSDB_IDL_ALERT is also set, then
> the
> + * IDL will change the value returned by ovsdb_idl_get_seqno() when the
> + * column's value changes in any row.
> *
> * The possible mode combinations are:
> *
> - * - 0, for a column that a client doesn't care about.
> + * - 0, for a column that a client doesn't care about. This is the
> default
> + * for every column in every table, if the client passes false for
> + * 'monitor_everything_by_default' to ovsdb_idl_create().
> *
> * - (OVSDB_IDL_MONITOR | OVSDB_IDL_ALERT), for a column that a client
> wants
> - * to track and possibly update.
> + * to track and possibly update. This is the default for every
> column in
> + * every table, if the client passes true for
> + * 'monitor_everything_by_default' to ovsdb_idl_create().
> *
> * - OVSDB_IDL_MONITOR, for columns that a client treats as
> "write-only",
> * that is, it updates them but doesn't want to get alerted about its
> own
> * updates. It also won't be alerted about other clients' updates,
> so this
> * is suitable only for use by a client that "owns" a particular
> column.
> + * Use ovsdb_idl_omit_alert() to set a column that is already
> replicated to
> + * this mode.
> *
> * - OVDSB_IDL_ALERT without OVSDB_IDL_MONITOR is not valid.
> *
> @@ -124,8 +174,8 @@ const struct ovsdb_idl_table_class
> *ovsdb_idl_table_class_from_column(
> * that a client wants to track using the change tracking
> * ovsdb_idl_track_get_*() functions.
> */
> -#define OVSDB_IDL_MONITOR (1 << 0) /* Monitor this column? */
> -#define OVSDB_IDL_ALERT (1 << 1) /* Alert client when column updated? */
> +#define OVSDB_IDL_MONITOR (1 << 0) /* Replicate this column? */
> +#define OVSDB_IDL_ALERT (1 << 1) /* Alert client when column changes? */
> #define OVSDB_IDL_TRACK (1 << 2)
>
> void ovsdb_idl_add_column(struct ovsdb_idl *, const struct
> ovsdb_idl_column *);
> --
> 2.20.1
>
>
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